AbstractTissue kallikrein (KLK1) and the kallikrein-related peptidase (KLK2–15) genes encode for a subgroup of 15 homologous secreted serine proteases possessing numerous physiological roles, such as the regulation of blood pressure, hormone processing and tissue remodeling. The expression ofKLKsis detected in a broad spectrum of human tissues where it has been found to be regulated mainly by steroids hormones. The aberrant expression ofKLKs, presented in many human malignancies, highlights the significance of this gene family for early diagnosis, prognosis and monitoring of cancer patients, as it is strongly emphasized by the routine use of PSA (KLK3) for prostate cancer management. Here, we review the presently known data regarding the role ofKLKsas cancer biomarkers, giving emphasis on novel information about the subject.